Blood Vessels - Learning Objectives

Define blood flow, blood pressure, and resistance; explain the relationships between these. Know the mathematical formula showing the relationship among these three (Ohm's Law).

- blood flow: volume of blood flowing through vessels, organ, or entire circulation in given period. - blood pressure: force per unit area exerted on wall of blood vessel by blood. - resistance: the oppositon to flow. - Ohm's law?

Be able to map the pathway of formation of angiotensin II starting with angiotensinogen (Renin-Angiotensin-Aldosterone Pathway). List the specific effects of angiotensin II, aldosterone, and antidiuretic hormones on blood volume and/or blood vessel diameter.

- kidneys are stimulated to release renein. - liver secretes angiotensionogen. - renin turns angiotensinogen into angiotensin I. - angiotension I is converted by the enzyme ACE to create Angiotensin II. - Angiotensin II is a constrictor of all blood vessles which causes blood pressure to go up. - Angiotensin II acts on the adrenal gland for stimulate release of Aldosterone. - Aldosterone stimulates the reabsoprtion of sodium and water. - Sine we are retaining more water, we are increasing blood pressure.

The Baroreceptor Reflex

- this is caused by the stretch or lack of stretch of barorecptors. __________________________ - Drop in Arterial blood pressure. - This causes inhibition of the barorecptors (no strecth when blood pressure is low) in the carotid sinsuses and aortic arch. - activation of the cardioacceleratory center. - inhibition of cardioinhibitory center. - stimulation of vasomotor center. - decrease in parasympathetic stimualtion and an increase in sympathetic stimulation, heart rate, contractiltiy, and cardiac output. - Causes a Sympathetic Stimulation of vasoconstriction. __________________________ - Increase in arterial blood pressure. - activation of the barorecpetors in the carotid sinuses and aortic arch. - inhibtion of the cardioacceleratory cente. - activation of the cardioinhibitory center. - inhibiton of vasomotor center. - causes an increase in parasympatheric stimulation. - decrease in sympathetic stimulation, decrease in heart rate, decrease in contractilty. and decrease in cardiac output. - Causes a decrease in sympathetic stimulation or vasodilation. ______________________________ - Atrial blood pressure increases. - Activation of the barorecptors in the carotid sinuses and aortic arch. - Inhibition of the cardioaccelteratory center. - Activation of the cardioinhibitary center. - Inhibition of vasmotor center. - Increases parasympathetic stimulation. - Sympatheric stimulation decreases, HR decreases, contractilty decreases, and cardiac output decreases. - Sympathetic stimulation of vasodilation.

Define vasoconstriction and vasodilation. Indicate which tunic changes vessel diameter for this function.

1 - vasoconstriction: decreased lumen diameter 2 - vasodilation: increased lumen diameter. - the tunic that changes vessel diameter is the TUNICA MEDIA.

Compare and contrast the structure and function of the three types of arteries (elastic, muscular, and arterioles).

1) Elastic arteries 2) Muscular arteries 3) Arterioles _______________________ Elastic Arteries: - thick walled with large, low resistance lumen. - elastin is found in all three tunics, mostly tunica media. - contain substantial smooth muscle, but inactive in vasocontriction. - act as pressure reservoirs that expand and recoil as blood is ejected from heart. - allows for continous blood flow downstream even between heartbeats. - elastic arteries will give rise to muscular arteries. ___________________________ Muscular Arteries: - have thickest tunica media with more smooth muscle, elastic tissue. - tunica media sandwhiched between elastic membranes. - active in vasocontriction, - deliver blood to specific organs. - distributing arties because they deliver blood to body organs. - diameters range from pinky-finger size to pencil-lead size. - Account for most of named arteries. ____________________________ Arterioles - smallest of all arteries - larger arterioles contain all three tunics. - smaller arterioles are mostly single layer of smooth muscle surrounding endolithelial cells. - control flow into capillary beds via vasodialation and vasocontriction of smooth muscle. - are considered resistance vessels because they control blood pressure and flow in response to neural and hormonal stimulaion. - local chemical changes.

Explain the three major sources of resistance and explain why vessel diameter is considered as the major determinant of vascular resistance.

1. Blood viscosity: thickness (stickiness) of blood due to formed elements and plasma proteins. - more viscous blood prolongs friction, which is correlated with low pulsatile pressure. - we need to increase pulsatile pressure in order to get the blood moving. - we cannot change blood viscosity. (only if it is a disease) 2. Total blood vessel length: longer the vessel, more friction. - need to increase pulsatile pressure near the heart in order to fix this. - we cannot change the length of the circuit. (this only happens during growth). 3. Blood vessel diameter: radius increases, resisatnce decreases. - greatest influence on resistance. - the larger the diameter, the less pressure on the walls of the vessels. - we change the diameter through vasoconstriction and vacodilation. This is controlled by the tunica media. - aretries can control the blood flow in our body... especially in the arterioles.

Describe how blood pressure differs in the arteries, capillaries, and veins.

Arteries: there is high blood pressure within the arteries since elastic arteries are able to recoil and initiatillay start of the circulatory system with a higher pressure. This pressure will decrease as it progresses to the capillaries. Capillaries: there is a constant pressure and flow throughout the capillaries. Veins: the venous system is a low pressure system.

Define local tissue perfusion, in contrast to systemic blood flow. Describe how the autoregulation mechanisms listed below affect local tissue perfusion: myogenic controls and metabolic controls (NO, pH, CO2, O2)

Intrinsic Controls: signals prodcued by the organ itself to contrict or relax arterioles within the organ. - Vasodilator signals: Low O2, High CO2, High pH, Prostaglandins, adenosine, nitric oxide (NO). - Vasoconstrictor signals: blood vessel stretch causes vasoconstriction (myogenic tone) endothelins ___________________________ Extrinsic contrrols: - neural and hormonal - control blood pressure -redistribute blood during exercise and thermoregulation

Describe the three layers (tunics) that form the wall of a blood vessel, their tissue types, and function of each.

Tunica intima: this is the innermost layer that is in "intimate" contact with blood. - is made up of endolithium which is simple squamous epithelium tissue. - continous with endocardium. - slick surface reduces friction. - also has a subendolitheal layer that is made up of connective tissue. ____________________________ Tunica media: middle layer compsed mostly of smooth muscle and sheets of elastin. - sympathetic vasomotor nerve fibers innervate this layer. - SNS controls vasoconstriction and vasodilation. - bulkiest layer responsible for maintain blood flow and blood pressure. _____________________________ Tunica externa: outermost layer of wall. - composed mostly of loose collagen fibers that protect and reinforce surrounding sturctures. - has nerve fibers and lympathic vessels. - large veins will contain elastic fibers. - includes the vasa vasorum which is a system of tiny blood vessels found in larger vessels. They function to nourish the outermost external layer.

Describe the regulation of blood pressure by the autonomic nervous system, understanding the effects of each of the following on heart rate, ventricular contraction, and blood vessel diameter: cardiac control and vasomotor centers, sympathetic and parasympathetic nervous system, chemoreceptors, and baroreceptors.

We need to regulate pressure... in order to prevent too high and too low of blood pressure. - we can compensate for this by vasoconstriction and through vasodialation controlled by the tunica media. - vasodilation = decreases blood pressure - vasoconstriction = increases blood pressure. - we can change blood pressure by changing the peripheral resistance (this affects the flow which is affected by diameter, blood viscosity, and length) and through cardiac output (stroke volume and heart rate). _______________________ Neural Regulation: short-term (minute to minute) regulation of the blood pressure. __________________________ - sympatheric stimulation in heart. - SA nodes (increased HR) and cardiac myocytes (increased contractility and increased stoke volume) - This sympathetic stimulation will cause an increased cardiac output. - parasympathetic stimulation in the heart will decrease the action of the SA and AV nodes which will decrease heart rate and decrease cardiac out put. ___________________________________ - sympathetic stimulation in the vessels. - veins will go through vasoconstriction which will increased venous return to the heart. - the increased venous return causes pre-load which will increase cardiac output which will then lead to increased blood pressure. - arterioles will go through vasoconstriction which will increase the total peripheral resistance which will then increase blood pressure. ____________________________ How are these neural stimualations regulated? - they are regulated through baroreceptors (stretch recepters in the cartid sinuses) and chemoreceptors (recpetors of CO2, O2 and pH in the aortic arch and large arteries of the neck. - they work through the cardiovascular centers in the medulla oblongata. - this is a negative feedback mechanism.

Understand the direct and indirect (hormonal) regulatory mechanisms used by the kidneys to control mean arterial blood pressure.

We need to regulate pressure... in order to prevent too high and too low of blood pressure. - we can compensate for this by vasoconstriction and through vasodialation controlled by the tunica media. - vasodilation = decreases blood pressure - vasoconstriction = increases blood pressure. - we can change blood pressure by changing the peripheral resistance (this affects the flow which is affected by diameter, blood viscosity, and length) and through cardiac output (stroke volume and heart rate). ______________________________ Hormonal Regulation: _____________________________ - Stress will cause the adrenal gland to secrete epinephrine and norepinephrine. - this will cause vasoconstriction (leading to a smaller lumen) which will increase the total peripheral ressitance. - increased blood pressure. ___________________________ - Decrease in Blood Pressure/Volume. - This will cause renin secretion by the kidneys. - Renin will stimulate ACE to turn Angiotensinogen to Angiotensin which will cause vasoconstriction. This will cause increased total peripheral resistance which will increase blood pressure. _________________________________ How do we inhibit high blood pressure or vasconstriction. - increase in volume causes heart to release ANP. - ANP from the heart will stimulare vasodilation. - this causes a decreade in peripheral resistance.

Describe the structure and function of a capillary bed. Understand the roles of pre-capillary sphincters in controlling blood flow through capillaries.

capillary bed: interwoven network of capillaries between arterioles and venules. - function in microcirculation which is the flow of blood through bed from ateriole to venule. - composed of a terminal arteriole and postcapillary venule. - the flow through bed is controlled by diameter of terminal arteriole and upstream arterioles. - local chemical conditions and arteriolar vasomotor nerve fibers regulate amount of blood entering the capillary bed. - arteriole and terminal arteriole dilated when blood needed, contricted to shunt blood away from bed when not needed. - vascular shunt: channel that directly connects arteriole with venule (bypasses true capillaries) - consists of metarteriole and throughfare channel. - precapillary sphincter: cuff of smooth muscle surroinding each true capillary that branches of arteriole; acts as a valve regulating blood flow into capillary bed. - controlled by local chemical conditions and is not innervated.

Describe the different mechanisms of molecule transport (paracellular vs transcellular, active vs passive) across the capillary bed.

depends on the types of capillary. - high to low concentration (passive diffusion) - water soluble: paracellular, facilitated transport, pincytosis (intercellular clefts allow for the movement of intracellular substance) - lipid soluble: simple diffusion - the size of the particle matters: paracellular = small particles, pinocytotic transport = large particles

Define hydrostatic pressure and osmotic pressure. Explain how the differences in these pressures determine the movement of water and solutes between blood and the interstitial fluid across the capillary wall along the capillary bed.

hydrostatic pressure: pressure exerted by the fluid inside the capillary against the wall. - more hydrostatic pressure the more fluid leaks out of the vessel. - hydrostatic pressure drops along the capillary. osmotic pressure: pressure caused by the solutes that cannot leak out of the vessel (proteins) - more osmotic pressure = more fluid gets sucked in to the vessel. - the osmotic pressure reamins constant (proteins cannot go anywhere) ______________________ Hydrostatic pressure in capillary pushes fluid out of the capillary while the osmotic pressure in capillary pulkls fluid into the capillary.

Compare and contrast the structure and function of the three types of veins (venules, medium and large veins). Understand their role as a blood reservoir.

veins: carry blood toward the heart. - formation begins when capillary beds unite in postcapillaty venules and merge into larger and larger veins. - Venules: consist of endolithum and few pericytes, - very porous, allow fluids and WBCs into tissues/ - larger venules will have one ro two layers of smooth muscle cells. _____________________________ veins are formed when venules converge. - have all tunics, but thinner walls with large lumens compared with corresponding arteries. - tunica media is thin, but tunica externa is thick. - contain collagen fibers and elastic networks. - large lumen and thin walls are good storage vessels. - capacitance vessels = blood reservoirs = veins. - blood pressure is lower than in arteeries so aspation are made to ensure return of blood to heart. - the large diamters lumens offer little ristsance. - venous valaves prevent the backflow of blood and these are most abundant in veins of limbs.